Liquid Penetrant also known as dye penetrant testing is a nondestructive test method using a visible or fluorescent die that causes bleed out from the discontinuity.
The process is based upon capillary action, where low surface tension fluid penetrates into clean and dry surface-breaking discontinuities. Penetrant may be applied to the test component by dipping, spraying, or brushing. After adequate penetration time has been allowed, the excess penetrant is removed and a developer is applied. The developer helps to draw penetrant out of the flaw so that an invisible indication becomes visible to the inspector.
Types of flaws that can be detected with PT
This method is used to detect surface-breaking defects.
Types of material that can be tested with PT
Liquid Penetrant can be used on metals, plastics, or ceramics and can be applied to non-ferrous and ferrous materials.
Advantages of using PT
There are many positive aspects to using PT, a few key points include:
- Testing is portable and cost-effective
- It can easily be used on small and large surfaces
- It can be used indoors or outdoors
- Parts with irregular shapes or complex geometries can be tested using this method
- Indications are visible directly on the components surface
Disadvantages of using PT
Although Dye Penetrant Inspections are a great tool, it is important to remember a few things:
- Only detects surface breaking defects
- Test material must be nonporous
- Pre-cleaning is critical – contaminants can mask defects
- Post cleaning can be required to remove chemicals
- Chemical exposure/handling precaution considerations should be given
- Machining, grinding and other processes can cause metal smearing which can inhibit detection of flaws and defects
- Some materials may require etching prior to inspection
Industries that use PT
PT can be used in many industries including:
- Structural Steel
- Power Generation